1. Field of the Invention
The present invention relates to an electromagnetic drive unit for use in a relay apparatus and a polarized relay of the type in which relay contacts are driven by a movable member or block adapted to be operated through energization of the electromagnetic drive unit.
2. Description of the Prior Art
In a known polarized relay apparatus, the contacts are operated by means of a drive mechanism which comprises such an electromagnetic drive unit or assembly as shown in FIG. 1 of the accompanying drawings. Referring to the figure, the electromagnetic drive assembly is composed of a permanent magnet 1 and a pair of inverted C-like armature plates 2 and 3 between which the permanent magnet 1 is interposed such that the axis of magnetization of the permanent magnet 1 extends perpendicularly to the armature plates 2 and 3. A bar-like iron core 5 wound with the coil 4 is disposed between the armature plates 2 and 3 with both ends of the core 5 being positioned in the air gaps defined, respectively, by the opposing end poles of the armature plates 2 and 3. When a current is supplied to the coil 4, the armatures 2 and 3 are rotated about a pivotal shaft 6 in either one of derections indicated by a double-head arrow S depending on the direction of the supplied current, whereby a movable contact plate or piece of a contact mechanism is operated in the direction to open or close the contacts. The prior art electromagnetic relay shown in FIG. 1 however suffers from drawbacks mentioned below. In the present state of technology in the concerned field, the electromagnetic relay tends to be miniaturezed so that it can be mounted on a substrate for a printed circuit. In this connection, it is noted that the whole length of the known electromagnetic drive unit or assembly is necessarily increased due to the fact the air gaps for allowing movement of the armatures 2 and 3 are provided at both ends of the iron core 5 wound with the coil 4. Further, because the coil assembly is disposed as overlying the armature block of a substantial thickness, an increase in height is involved, resulting in a bulky structure which prevents effective miniaturization of the electromagnetic relay. It should further be added that there is a great distance between the permanent magnet 1 and each of the air gaps, giving rise to significant leakage of the magnetic flux and hence low sensitivity of the electromagnetic relay.
As another example of the electromagnetic drive unit for the polarized relay apparatus, there has been known a structure in which an E-like iron core is employed (reference may be made to Japanese Patent Publication No. 30232/1982, by way of example.) According to this prior art, an E-like iron core 7 having three legs 7a, 7b and 7c is used, wherein the mid leg 7b is wound with the coil 4, as is shown in FIG. 2 of the accompanying drawings. A C-like movable element block generally denoted by 12 is constituted by a permanent magnet 9 sandwiched between two pole pieces or plates 10 and 11 with the axis of magnetization of the magnet 9 extending perpendicularly to the pole pieces 10 and 11. The legs or free ends of the pole pieces are, respectively, disposed within air gaps (also referred to as the working gaps) 8 defined by the three legs 7a, 7b and 7c of the E-like core 7. When the coil 4 is electrically energized in one direction, the movable element or block 12 is moved to the right as viewed in FIG. 2, to form a closed magnetic circuit. On the other hand, when the coil 4 is supplied with a current in the other direction, the movable block 12 is displaced to the left, whereby the contacts are closed or opened in response to the movement of the block 12 to which the contact mechanism is connected. This electromagnetic assembly is disadvantageous in that width of the assembly is remarkably increased, thus it is difficult to incorporate the electromagnetic relay in electronic and electric apparatus which are increasingly required to be implemented in a miniature size. Such large width may be explained by the fact that, assuming the required magnetic path cross-sectional area of the center leg 7b wound with the coil 4 to be represented by a, the total cross-sectional areas of three legs 7a, 7b and 7c amounts to 3 X a. The lateral dimension or width of the electromagnetic drive assembly is therefore enlarged, which is further compounded by the necessity of provision of the working air gap 8 which encloses the coil 4.